1. Field of the Invention
This invention relates to a process for producing an alkenylbenzene efficiently in and safely by the reaction of an alkylbenzene and a conjugated diolefin in the presence of an alkali metal. More specifically, this invention relates to a process for producing an industrially useful alkenylbenzene. For example, 5-(o-tolyl)-pentene, an alkenylbenzene obtained by reacting o-xylene with 1,3-butadiene can be converted into naphthalenedicarboxylic acid which is useful as a high-molecular weight starting material by a reaction sequence in which 5-(o-tolyl)-pentene is cyclized into dimethyltetralin, and said dimethyltetralin is dehydrogenated into dimethylnaphthalene which is then oxidized into naphthalenedicarboxylic acid.
2. Description of Related Art
There has been so far known a process for producing an alkenylbenzene by the reaction of an alkylbenzene and 1,3-butadiene in the presence of an alkali metal (see U.S. Pat. No. 3,244,758).
The above process, however, suffers a defect that if an alkenylbenzene is obtained in high yield, costly metallic potassium has to be used in a large amount.
Further, in order to solve this problem, a process has been proposed in which when metallic potassium and metallic sodium are conjointly used as a catalyst in blowing 1,3-butadiene into an alkylbenzene for reaction, costly metallic potassium may be used in a small amount (see Japanese Patent Publication No. 34,570/1981 and U.S. Pat. Nos. 3,766,288 and 3,953,535).
Still further, an improved process has been proposed in which the reaction of o-xylene and butadiene is performed in a fixed bed with metallic potassium supported on potassium carbonate or alumina (U.S. Pat. No. 4,990,717).
These processes are, however, all processes directly using metallic potassium. Metallic potassium is highly reactive with air, oxygen, water, etc., fires only when contacting these substances and is a potential fire hazard. Especially, a sodium (Na-K) alloy is highly reactive with oxygen and water, burning on contact with traces of oxygen, water, etc., and being quite dangerous in the presence of inflammable substances (oils).
In British Patent No. 1,269,280, it is stated that in a side chain alkylation reaction of aromatics with olefins using sodium and an anhydrous potassium compound as a catalyst, a diene hinders the reaction.
Japanese Laid-open Patent Application (Kokai) No. 263,643/1986 involves a process in which toluene is alkenylated with butadiene using metallic sodium and anhydrous potassium sulfate as a catalyst.